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Promethium
'''Promethium '''is a chemical element with the symbol Pm and atomic number 61. It is notable for being the only other exclusively radioactive element besides technetium, which is followed, by chemical elements that have stable isotopes. Uses include, a radiation source for thickness gauges, as a light source for signals that require reliable, independent operation (using phosphor to absorb the beta radiation and produce light). In particular, Promethium(III) chloride (PmCl3) mixed with zinc sulphide (ZnS) was used for a time as a major luminous paint for watches after radium was discontinued. This mixture is still occasionally used for some luminous paint applications (though most such uses with radioactive materials have switched to tritium for safety reasons).In a nuclear battery in which cells convert the beta emissions into electric current, yielding a useful life of about five years, using Pm-147. Promethium has possible future uses in portable X-ray sources, and as auxiliary heat or power sources for space probes and satellites (although the alpha emitter plutonium-238 has become standard for most space-exploration. Characteristics Promethium's longest-lived isotope 145Pm is a soft beta emitter with a half-life of 17.7 years. It does not emit gamma rays, but beta particles impinging on elements of high atomic numbers can generate X-rays, and a sample of 145Pm does produce some such soft X-ray radiation in addition to beta particles. Pure promethium exists in two allotropic forms, and its chemistry is similar to other lanthanides. Promethium salts luminesce in the dark with a pale blue or greenish glow, due to their high radioactivity. Promethium can be found in traces in some uranium ores, as a fission product. Newly made promethium is also seen in the spectra of some stars. Promethium metal tarnishes slowly in air and burns readily at 150 °C to form promethium(III) oxide, it is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form promethium hydroxide. The metal reacts with all the halogens. Promethium dissolves readily in dilute sulphuric acid to form solutions containing the pink Pm(III) ions, which exist as a Pm(OH2)93+ complexes. Thirty-six radioisotopes of promethium have been characterized, with the most stable being 145Pm with a half-life of 17.7 years, 146Pm with a half-life of 5.53 years, and 147Pm with a half-life of 2.6234 years. All of the remaining radioactive isotopes have half-lives that are less than 364 days, and the majority of these have half lives that are less than 27 seconds. This element also has 11 meta states with the most stable being 148Pmm (T½ 41.29 days), 152Pmm2 (T½ 13.8 minutes) and 152Pmm (T½ 7.52 minutes). The isotopes of promethium range in atomic weight from 127.9482600 u (128Pm) to 162.9535200 u (163Pm). The primary decay mode before the longest-lived isotope, 145Pm, is electron capture, and the primary mode after is beta minus decay. The primary decay products before 145Pm are neodymium (Nd) isotopes and the primary products after are samarium (Sm) isotopes. Along with technetium, promethium is one of only two elements with atomic number less than 83 that have only unstable isotopes, which is a rarely occurring effect of the liquid drop model and stabilities of neighbor element isotopes. Value The base value of each unit of ranges between 15 and 45Ð per unit, with up to 2 units being found at any one time. Presence on Mars: Very Rare Category:Chemical elements